Transformer



L. F. BLUM E TRANSFORMER April 1, 1930.

llllllllllllll Illlllllllllll.

lllllllllllllf lllllllllllll Illlllllllllll lmmullul Filed Nov. 28, 1928 Inventor`- Louis Flume, by MMT/Zweed@ H s Attorney.

mmm/mmmemmmmmm Mmmm Patented Api'. 1, 1930A UNITED STATES PATENT oEFicE LOUIS F. BLUME, OF

'.PITTSFIELD, MASSACHUSETTS, ASSIGNOR TO GENERAL ELEGIBIC COMPANY, A CORPORATION F NEW YORK- 'rnANsronnEn l Application led Novemper 28, 1928. Serial No. 322,415.

My invention relates to transformers and more particularly to transformers provided with auxiliary windingsy for supplying current to operate voltage and current responsive devices lsuch as voltmeters, ammeters and relays. The voltage at which the main windings invention s to provide a transformer with an improved arrangement of windings for controlling an indicating or other instrument, these windings being magnetically associated with the main windings of the transformer but well separated from them so that very little insulation is necessary.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which Fig.' 1 shows the invention as a plied in connection with a shell type'trans ormer having concentric cylindrical windings;`Fig. 2 shows the invention applied in connection with a shell type transformer having interleaved windings; Fig. 3 shows the invention applied in connection with a core type transformer; Fig. 4 shows a transformer similar to that shown in Fig. 3- with the invention ap# plied in a diferent manner; Fig. 5 indicates the windings shown in Fig. 1 with the paths of magnetic iux produced by the main transformer currents; and Fig. 6 is an explanatory vector diagram of magnetic iuxes.

Likes reference characters indicate similar parts in the different figures of the drawing.

The transformer shown in Fig. 1 is of the shell type having a magnetic core with a central winding leg 10 and two outer legs 11 and 12 joined at their ends by yokes. The winding leg 10 is surrourded by concentric cylindrical windings 13 and 14. The currents in the main windings 13 and 14 induce magnetic {'lux which takes several paths as indicated in Fig. 5 where the paths at one side of the core only are shown, there being a similar disposition of flux of course vat the other side of the core if the two` sides of the transformer are symmetrical as is usually the c ase.

The invention may be bestk understood by considering 4that there are two magnetic iiuxes. The magnetizing current induces a main flux @u which is indicated by a broken line in Fig. 5. This flux @M flows entirely in the magnetic core and links both of the main windings 13 and 14. The two load currents in the windin s 13 and 14 induce the other magnetic flux L which is indicated by full lines in Fig. 5. `This iux (DL, usually called the leakage flux, ilowsthrough the space between the windings 13 and 14 and returns Ain what may be considered as four separate parts 0A, Qtr, @B and 0s. As indicated in Fig. 5, the flux (Z) A links the winding 13 and iiows entirely in the core, the flux @fr links the winding 13 and flows through the space between this vwinding and the winding leg 10 of the core, the flux @B links the winding 14 and flows entirely in the core, and the flux @s links the winding 14 and flows outside of the core. The phase relations of these fluxes will not be the same for all load conditions but are determined by the power factor of the load. They may be represented by a vector diagram such as is shown in Fig. 6.

An important characteristic of the leakage iiux or of any part of it is that its value is substantially proportional to the load on the transformer. Any of the leakage fluxes which have been mentioned can therefore be used as a measure of this load. This result is attained by auxiliary windings connected to a suitable instrument such as an ammeter.

In the arrangement shown in Fig.` 1, an auxiliary winding 15 surrounds the winding leg 10 of the core and an auxiliary windin 16 surrounds each of the outer legs 11 an 1Q of the core. These auxiliary windings need to have only a few turns each so that the voltages induced in them are low and they are also close to the core so that they are easily insulated from the main windings 13 and 14. There is also no danger from high voltages in the circuit or in the instrument 'to which these auxiliary windings are connected. The auxiliary windings 15 and 16 are connected in series to supply currentto a suitable connected and the numbers of turns in them are so proportioned that the voltage in the winding due to the main' ux @M is e ualA and opposite to the voltage in the win ing 16 due to the main fiux) @1.1. The volta e at the instrument 17 due to the main iiux M is therefore zero'. The total ux @la in the winding 13 is the vector sum of the iiuxes @15 and @qu The total iiux @14 in the winding 14 is the vector sum of ythe fluxes @16 and @5.

. The voltages in the windings 15 and 16 due iliary not equal an' -o to the return leakage iiuxes @A and @B will be added together, however, as will be clear from a consideration of the relative directions of themain andA leakage iiuxes shown by the arrows in Fig. 5. The instrument 17 will therefore be responsive to 4a voltage which is proportional to the leakage iux and therefore to the load on the transformer.v

The transformer shown in Fig. 2 is of the l shell type with interleaved windings 13 Vand 14.. The auxiliary windings 15 and 16 are similar to the windings 15 and 16 of Fig.

1 and are similarly connected, the winding 16 being disposed on the upper'yoke at opposite sides of the winding leg, however, instead of on the outerlegs of the core. It is obvious that ithe main flux @M will induce e ual and opposite voltages in the auxiliar' wmdings sothat the voltage at the terminals of the circuit due to this main iiux will be zero.

lt is also clear that the currents in the two mam windings 13 and 14 will induce a leak` age lux in the spacesbetween these windings and which will link the auxiliary winding 15 but not the auxiliary winding 16. This leakage flux will therefore induce in the aux- .15 and 16 voltages' which are posite so that a voltage due ux and therefore proportionon the transformer will be availto the leaka e al to the loa able to operate an instrument connected tov the auxiha circuit.

In both o `the arrangements shown in Figs.

of the core insteady of being connected together as a single winding on one side of the core. .The arrangements'shown are considered preferable in case of possible unbalance `.fin the two magnetic circuits through the 60 outer legs of the core.

AThe transformer shown in Fig. 3 is of the core type with concentric cylindrical mam f windings 13 and 14. The auxiliary winding `15 surrounds one of the winding legs of the core and -a single winding 16 surrounds the winding 16 is showni of -UT to OT, the

and each surrounds the path of themain ux @M so that the voltages induced by the main ux are equal and opposite. It is obvious that the leakage uxes lg the two windings 15 and 16 will not be equal and opposite, however, and a'ain there will be a voltage induced by the eakage Eux in the auxiliary circuit for operating an instrument` and this voltage will be proportional to the load on the transformer.

ln accordance with a modification of the invention, the auxiliary windingsl and 16 may be arranged andconnected to gfve a voltage which is proportional to the voltage of either of the main transformer windings 13 and 14.4 It will be apparent that an instrument such as a `voltmeter, properly adljusted or calibrated, may be connected to the auxiliary windings instead of to one or ythe other of the main windings with much less diiliculty with insulation. Fig. 4 shows this modification of the arrangement shown in Fig. 3 Vand it will be apparent that similar modifications of the arrangements of Figs.

. 1 and 2 may be made.

posed. To obtain a voltage proportional to 'that of either of the main windin s, however, the relative numbers of turns in t e auxihary windings is different from that which has been described 'to give a voltage proportional to the transformer load. The main and leakage iuxes shown in Fig. 5 may be represented by a vector diagram such as 1s show in Fig. 6. In addition to the vectors4 re resenting the main and leaka e fiuxes, Fi .6 also includes a line SR which is paralle to the vector @la and whichmeets the vector @15 extended at R. It also includes a line UTwhich is parallel to the vector @1,5 and which meets the vector @16 extended at T.

To obtain a voltage proportional to that of the main winding 13, the numbers of turns N15 and N10' in the auxiliary windings 15 and 16 respectively are proportioned so that the ratio of @MNH t0 @NNN is equal to the ratio of OR to SR, the two windm s v15 and 16 being also connected so that t eir voltages are opposed. This result is apparent from the vector diagram of Fig. 6, bearing in mind that the voltage of a winding is proportional winding and the iux which links it. In like manner, a voltage proportionalto that of the main winding 14 is obtained by roportioning the numbers of turns N15 and)N16 in the auxiliary windings 15 and 16 `so that the ratio of @MNM to @MNH is equal to the ratio windings 15 and 16 being connected with their voltages opposed.

It is usually dicult to calculate accurately the distribution ofthe leakage flux of a transformer so that it may be diiicult in some cases to predetermine just what should be the relation or roportion between the numbers of turns in t e two auxiliary windin s 15 and 16 to give the desired result. The oregoing description demonstrates that the desired result will follow with the numbers of turns correctly proportioned between the two auxiliary windings and, if desired, the correct proportion may be ascertained by trial. T 1e invention has been explained b describinv and illustrating various mo ications thereof and it will be apparent that further changes and modifications may be made without departing from the scope of' the invention as defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. A transformer includin a `magnetic core having a winding le an an outer section for return magnetic ux, main windings on said winding leg, an auxiliar winding on said windin leg, and a secon auxiliary Winding on sai outer section of the core, the turns of said auxiliar windings being connected in series with the voltage of the turns on the winding leg opposed to the voltage of the turns on the outer section of the core.

2. A transformer includin a magnetic core having a winding leg an an outer section for return magnetic ux, main y rimary and secondary windings on said win g leg, an auxiliary winding on said winding leg, and a second auxiliary windin on said outer section of the core, said auxi iary windings being connected in series with their voltages opposed, and the numbers of turns in said two auxiliary windings being proportional to two vector components of a voltage proportional to an electrical condition in one of said main windings.

3. A transformer includin a magnetic core having a winding le an an outer section for return ma etic ux, main rimary and secondary win ings on said win ing leg, an auxiliary winding on said winding leg, and a second auxiliary winding on said outer section of the core, said auxiliary windings being connected in series with their voltages opposed, and the numbers of turns in said two auxiliary windings bein pro ortional to two vector components of t e vo tage of one of said main windings.

In witness whereof, I have hereunto set my hand this 26th day of November, 1928.

LOUIS F. BLUME.

lau 

